As you can see, cats don't age like dogs at all.
Can't give you any scientific explanations unfortunatly, this is just how I learnt it Dogs sort of grow old like us humans, gradually. Cats can seem young "forever" and then suddenly, almost overnight, they are very old indeed.

There were no public health laws in Ankh-Morpork. It would be like installing smoke detectors in Hell.
- Feet of clay.